NICER X-Ray Observations of Seven Nearby Rotation-powered Millisecond Pulsars
Chakrabarty, Deepto; Bogdanov, Slavko; Deneva, Julia S.; Ray, Paul S.; Wolff, Michael T.; Arzoumanian, Zaven; Guillot, Sebastien; Ho, Wynn C. G.; Guillemot, Lucas; Theureau, Gilles; Kerr, Matthew; Webb, Natalie A.; Jaisawal, Gaurava K.; Gendreau, Keith C.; Bult, Peter; Malacaria, Christian; Strohmayer, Tod E.; Miller, M. Coleman; Ransom, Scott; Wood, Kent S.; Cognard, Ismael
France, United States, United Kingdom, Denmark
Abstract
The Neutron star Interior Composition Explorer observed several rotation-powered millisecond pulsars (MSPs) to search for or confirm the presence of X-ray pulsations. When broad and sine-like, these pulsations may indicate thermal emission from hot polar caps at the magnetic poles on the neutron star surface. We report confident detections (≥4.7σ after background filtering) of X-ray pulsations for five of the seven pulsars in our target sample: PSR J0614-3329, PSR J0636+5129, PSR J0751+1807, PSR J1012+5307, and PSR J2241-5236, while PSR J1552+5437 and PSR J1744-1134 remain undetected. Of those, only PSR J0751+1807 and PSR J1012+5307 had pulsations previously detected at the 1.7σ and almost 3σ confidence levels, respectively, in XMM-Newton data. All detected sources exhibit broad sine-like pulses, which are indicative of surface thermal radiation. As such, these MSPs are promising targets for future X-ray observations aimed at constraining the neutron star mass-radius relation and the dense matter equation of state using detailed pulse profile modeling. Furthermore, we find that three of the detected MSPs exhibit a significant phase offset between their X-ray and radio pulses.